For Immediate Release
September 8, 2000

OUT
OF TIME: RESEARCHERS RECREATE 1665 CLOCK EXPERIMENT TO GAIN INSIGHTS INTO
MODERN SYNCHRONIZED OSCILLATORS

Undergraduate
researcher Matthew Bennett adjusts the pendulum of one clock under
study in this recreation of a 1665 experiment.
(300-dpi jpg version), 379k

While recovering from
an illness in 1665, Dutch astronomer and physicist Christiaan Huygens
noticed something very odd. Two of the large pendulum clocks in his room
were beating in unison, and would return to this synchronized pattern
regardless of how they were started, stopped or otherwise disturbed.

An inventor who had
patented the pendulum clock only eight years earlier, Huygens was understandably
intrigued. He set out to investigate this phenomena, and the records of
his experiments were preserved in a letter to his father. Written in Latin,
the letter provides what is believed to be the first recorded example
of synchronized oscillators – a physical phenomenon that has become increasingly
important to physicists and engineers in modern times.

More than 300
years after Huygens’ letter, physicists at the Georgia Institute of Technology
have recreated his original experiment. Beyond the historical curiosity,
the researchers hope this straightforward mechanical system of gears,
springs, weights and levers may help them gain insights into more modern
and complex synchronized oscillators.

"Having a
system available that lends itself to an intuitive and physical understanding
could be quite useful," said Dr. Kurt Wiesenfeld, a Georgia Tech
professor of physics. "We might be able to learn how this system
is like laser systems or superconducting electronic systems. If there
are general mechanisms affecting coupled oscillators, then perhaps we
can learn about these mechanisms by using the clocks as mechanical analogs
for electronic systems."

Dr.
Kurt Wiesenfeld and Dr. Michael Schatz are reflected in the pendulum
bob of one clock they are using to recreate the 1665 experiment of
Dutch physicist Christiaan Huygens.
(300-dpi jpg version), 379k

In particular, Wiesenfeld
says the clocks may offer a new way to look at a type of electronic device
known as a Josephson Junction.

"It’s a very
old-fashioned idea, not the way people who study coupled oscillators have
been thinking about nonlinear dynamics over the past decade or so,"
he added. "Classical physics still has things to teach us."

The system under
study consists of two spring-powered pendulum clocks attached to a wooden
platform with metal weights added. The platform is set on wheels, free
to move along a level metal track. Though the clocks are much smaller
than those built by Huygens, the relationship between the masses of the
pendulum bobs and that of the overall platform is similar. The clocks’
period – time between ticks – is also approximately the same.

The modern clock system
includes a feature not available to Huygens: laser monitoring that records
the pendulum swings for computer analysis.

So far, the clocks
have shown an ability to synchronize only in anti phase – that is, with
their pendulums swinging in opposite directions. This is true even when
the pendulums are started in-phase -- swinging in the same direction.
The 1665 letter recounts that Huygens also observed only anti phase synchronization,
helping confirm that the Georgia Tech researchers have successfully duplicated
his experimental conditions.

But the Georgia
Tech clocks also display behavior Huygens did not describe: what the researchers
call "amplitude death." Instead of synchronizing, one or both
pendulums ultimately stop moving altogether. This becomes more likely
as weight is removed from the platform carrying the clocks.

Working 20 years
before Sir Isaac Newton formulated the now-familiar laws of mechanics,
Huygens was hampered in his ability to explain what he saw. Because the
clocks are attached to a platform able to move, Huygens suggested that
the swinging of the pendulums somehow caused the platform to move "imperceptibly."
He also ruled out other theories, including the possibility that air currents
caused the synchronization.

Unlike Huygens,
Wiesenfield and collaborators Dr. Michael Schatz and undergraduate student
Matthew Bennett do have theories to explain what they see.

"In modern
terms, the general motion of pendulums can be roughly described as a combination
of in-phase and anti-phase synchronized motions, which are ‘normal modes,’"
explained Schatz, an assistant professor of physics. "A key feature
of our understanding of Huygens’ clocks is that the in-phase motion doesn’t
couple to the platform in the same way as the anti-phase motion. In-phase
motion can drive the very small platform movement, which drains energy
out of the system through friction between the platform and the surface
on which it rests."

But when the clocks
are synchronized in anti phase, the swinging pendulums balance each other,
generating no movement in the platform. This conserves their energy, thus,
providing a mechanism for favoring anti phase motion by the system, he
suggested.

"The heavier
the platform, the smaller the coupling between the two clocks," Schatz
said. "If it’s really heavy, the platform doesn’t move at all and
there is no coupling and no synchronization. But on the other hand, if
the platform is too light and there is too much motion, it will damp out
the clocks’ energy and create ‘amplitude death.’"

Despite the differences
introduced by improved clock-making, the fact that both systems display
stable anti phase synchronization shows the robustness of that feature,
Wiesenfeld pointed out.

Recreating the
system required considerable research that spanned not only 335 years,
but also two languages. Dr. Heidi Rockwood, chairperson of Georgia Tech’s
Department of Modern Languages, worked with Wiesenfeld to decipher the
original Latin -- which turned out to be not as scientifically clear as
the researchers had hoped.

"Only with
Kurt’s help did some of the passages make sense," said Rockwood.
"Since he understood the physics, he could ask questions like, ‘could
this mean such-and-such?’ And then things often fell into place."
From Rockwood, Wiesenfeld learned that the Huygens letter actually described
two different experiments.

But questions
remain. "There’s a lot of detective work in this," said Wiesenfeld.
"You can get some pieces of it, but you’re not sure what to fill
in. The more you think about it, the more you can imagine other possibilities."

PHOTO
COPYRIGHT INFORMATION:Photographs are copyrighted by the Georgia Tech Research Corporation and may be freely used by the news media with credit to the Georgia Institute of Technology. The photographer is Gary Meek , Georgia Tech Communications Division.